1. Field of the Invention
The present invention relates to cooling of a power converter and, in particular, relates to cooling of a power converter in which the direction of cooling air changes.
2. Description of the Related Art
Power converters such as a converter and an inverter are installed in an electric railway vehicle to drive a motor that drives the vehicle. These power converters perform power conversion by switching of semiconductor devices such as an IGBT (insulated gate bipolar transistor) and a GTO (gate turnoff thyristor).
In a semiconductor device, a conduction loss and a switching loss occur and are converted into heat. When this heat raises the temperature of the semiconductor device, there is a possibility of a reduction in conversion efficiency, a breakdown of the device, and the like. Therefore, it is necessary to cool the semiconductor device in such a way that the semiconductor device is in a predetermined temperature range. Since a power converter is mainly installed under the floor of a vehicle, for example, where the installation space is limited, it is necessary to cool a plurality of semiconductor devices efficiently with a small device configuration.
Here, the direction of traveling of the railway vehicle changes at a terminal and, when the railway vehicle travels forward and when the railway vehicle travels backward, equal heat is generated in any of these cases. In a cooler of a power converter, the cooler using a wind generated when the railway vehicle is running as cooling air, it is necessary to ensure cooling capability that does not depend on the direction of traveling. In the cooler of the power converter, the cooler using the wind generated when the vehicle is running for cooling, since a semiconductor device placed on the leeward side is cooled by the cooling air heated by the heat of a semiconductor device placed on the windward side, the temperature of the semiconductor device placed on the leeward side becomes higher than the temperature on the windward side. This makes it necessary to design the cooler in such a way that the temperature of the semiconductor device placed on the leeward side is in a predetermined temperature range. As a result, the semiconductor device placed on the windward side is cooled more than necessary, and the cooler increases in size as a cooler for the semiconductor device placed on the windward side.
JP-A-2003-298268 (hereinafter Patent Document 1) has a cooling air flow adjustment mechanism to cool a heating element efficiently and the cooling air flow adjustment mechanism has a shape in which the channel from the upstream side to the downstream side becomes narrow. With this shape, the cooling capability of a heat dissipation section provided in a downstream part is improved. Next, JP-A-2006-224796 (hereinafter Patent Document 2) provides, in a cooler of a converter for a railway, an air flow-guide plate for adjusting the volume of air which the cooler takes in to improve a trade-off between the time of low-speed driving in which only a small volume of wind generated when a vehicle is running is obtained in spite of high load and the time of high-speed driving in which, although the load is low, the volume of wind generated when a vehicle is running is large and cooling is performed more than necessary.
For example, a power converter for a railway vehicle, the power converter using, for cooling, a wind generated when the vehicle is running, needs to ensure cooling capability that does not depend on the direction of cooling air because the direction of the cooling air when the railway vehicle travels forward is reversed when the railway vehicle travels backward and equal heat is generated in any of these cases. Here, with the structure described in Patent Document 1, the cooling capability of the heat dissipation section provided on the downstream side is improved when the direction of the cooling air is one direction. However, when the direction of the cooling air is reversed, the cooling capability of the heat dissipation section provided on the downstream side is significantly reduced. This makes it impossible to eliminate the temperature difference between the semiconductor device placed on the windward side and the semiconductor device placed on the leeward side when the vehicle travels forward and when the vehicle travels backward. Moreover, although the existing technique described in Patent Document 2 can adjust the volume of air in accordance with the speed of the vehicle, this technique also cannot eliminate the temperature difference between the semiconductor device placed on the windward side and the semiconductor device placed on the leeward side when the vehicle travels forward and when the vehicle travels backward.